1. Field of the Invention
The present invention relates to a stereoscopic endoscope which can stereoscopically observe subject parts such as those inside body cavities and, in particular, to an improvement in configuration of an objective optical system disposed at the tip portion of its inserting portion.
2. Description of the Prior Art
Recently prevailing is a surgical technique in which endoscopes are used for observing subject parts within body cavities and performing operations of affected parts within the body cavities. In order to effect accurate diagnosis and alleviate sufferings of patients, the endoscopes have been technically being improved. In particular, in order to carry out more accurate diagnosis within a body cavity, it is useful to obtain depth information within the body cavity. Stereoscopic endoscopes have been known to respond to such a demand.
Known as such a stereoscopic endoscope is the one disclosed in Japanese Unexamined Patent Publication No. 8-122665, for example.
The endoscope objective optical system disposed at the scope tip of the stereoscopic endoscope disclosed in this publication comprises, successively from the object side, a pair of negative lenses disposed in parallel to each other, and a group of concentric positive lenses. As the number of lens sheets at parts which are separated into right and left sides is reduced, error between right and left images is minimized. Accordingly, the right and left images are easily merged with each other, whereby the fatigue of an observer is alleviated. Also, as a parallel negative lens pair is disposed at the leading end of the scope its positional adjustment is facilitated. Consequently, when assembling the endoscope, an optimal lens position for three-dimensional feel and eccentricity error adjustment of the right and left images can be easily set.
However, since the lens system at the leading end of the scope is constituted by a pair of negative lenses, and the positive lens group disposed downstream thereof commonly corrects aberrations of both luminous fluxes from the pair of negative lenses in the technique of the above-mentioned publication, it is not always satisfactory in terms of correction of astigmatism and image surface curvature.
In view of such circumstances, it is an object of the present invention to provide a stereoscopic endoscope which, in a simple configuration, can attain a highly accurate three-dimensional image in which aberration is corrected.
Also, there is a strong demand for minimizing relative deviation between the right and left images, which is a problem in stereoscopic endoscopes, such that the right and left images are easily merged with each other, thereby alleviating the fatigue of users. To this aim, it is necessary to enhance accuracy in positional setting of each of members disposed in the lens systems. Operations for actually aligning these members are complicated and likely to generate errors, however. Therefore, it has been required to minimize the number of members necessitating adjustment and facilitate their adjustment.
Further, while it is important for a stereoscopic endoscope to attain an image with a strong three-dimensional feel, a problem not to overlook is the fatigue of a user who continuously uses this stereoscopic endoscope for a long period of time in the case of an actual surgical operation. At the site of actual operation, information with a strong three-dimensional feel is not always necessary continuously from beginning to end. Instead, it is often the case that, after the state is accurately grasped, treatment can be effected while observing an image with a less three-dimensional feel.
It is another object of the present invention to provide an endoscope objective optical system which minimizes errors in right and left images or allows its user to adjust a three-dimensional feel, thereby alleviating the fatigue of the user caused upon image merging.
The present invention provides a stereoscopic endoscope comprising an elongated inserting portion; an objective optical system disposed within a tip of the inserting portion; and imaging means, disposed within the inserting portion, for capturing an object image formed by the objective optical system;
wherein the objective optical system comprises, successively from the object side, a first lens pair made of a pair of negative lenses disposed in parallel to each other, a second lens pair made of a pair of positive lenses disposed in parallel so as to respectively correspond to the lenses of the first lens pair, and a positive lens group.
Preferably, the lenses in the second lens pair in the objective optical system are concentric with their corresponding lenses in the first lens pair.
A stop or light-shielding plate may be disposed between the second lens pair and the positive lens group, while this stop or light-shielding plate, each lens constituting the first lens pair, and its corresponding lens constituting the second lens pair may be integrally formed as a half of a pair of members disposed in parallel.
Preferably, the pair of positive lenses constituting the second lens pair are movable symmetrically to each other in directions perpendicular to the optical axis of the positive lens group.